There is a tendency that sub-threshold leakage increases with the increase in size of semiconductor devices, which is called a hump phenomenon. As in two MOSFETs in which characteristics of an active region and corners of a device isolation layer (STI) are different, the hump phenomenon causes high leakage current under threshold voltage of a semiconductor device due to low threshold voltage at the STI corner-sided channel, such that various methods have been proposed to prevent the problem.
For example, one related method of preventing the hump phenomenon involves implanting a boron ion to the side wall of a trench and of preventing the hump phenomenon by improving rounding characteristics of the joint of an active region and an STI region. Although it may be possible to prevent hump characteristics, there is a problem that using these related methods increases cost due to introducing an additional process, or increases the area of devices.